The present invention is directed to an apparatus for forming a bulge in a stranded steel wire cable for use as an anchor in a concrete structural component. In forming the bulge, the cable is axially upset from one end over a portion of its axial length with the individual wires being deformed axially and spread radially outwardly. The apparatus includes an elongated frame with a clamping device at one end including a pair of clamping jaws and a thrust member at the other end. A piston-cylinder unit contacts the clamping device and is connected to the thrust member for effecting the axial displacement of the stranded cable. An upsetting pipe is located between the thrust member and the clamping device and is displaceable in the long direction of the frame. The thrust member and the upsetting pipe include means for affording rotation of the stranded cable during the upsetting operation.
In addition to steel rods, steel wires and steel wire cables, high strength stranded steel wire cables have been used increasingly in recent years as reinforcing elements, particularly in prestressed concrete. Such stranded cables include a central wire around which outer wires are wrapped in a symmetrical manner with regard to the central wire. In some instances, the stranded cable may include two annular layers of outer wires. The outer wires are twisted or wrapped as in a wire rope.
When such stranded cables are used as prestressing members or tendons, generally they are anchored by wedges. Wedge anchors are relatively costly in view of the material used as well as the time required for installation. Such costs are especially significant when the anchor is to be set in a concrete structural component in a fixed manner, that is, when the prestressing member is not required to be tensioned at the location of the anchorage. Moreover, it is difficult to obtain sufficient fatigue strength when using wedge anchors without employing additional measures.
For the fixed anchorage of stranded cables, that is, an anchorage which cannot be tensioned, it has been known to upset a stranded cable at one end by applying pressure so that the individual wires, while deforming in a plastic manner, form a bulge which can be embedded in a concrete structural component for anchoring the stranded cable. To produce such a bulge, an apparatus is known in which the bulge is formed along at least a part of its length with the maximum outside diameter located within an upsetting pipe extending coaxially relative to the stranded cable axis whereby the individual wires of the cable bear against the inside wall of the upsetting pipe during the formation of the bulge so that the wires unwind, note DE-OS 32 07 957 and corresponding U.S. Pat. No. 4,469,756. In this manner, a uniform, gradually increasing spatial curvature of the individual wires of the stranded cable can be achieved with a particularly large number of deflection angles affording an anchorage with a short axial length and very good fatigue behavior.
One problem in such upsetting apparatus is the clamping device used to hold the stranded cable during the upsetting operation. If clamping jaws are used, they are hydraulically driven making the apparatus, as a whole, very costly and cumbersome. The clamping force can be developed in a simpler manner by using wedges. If wedges are used for holding the stranded cable, however, they must be provided with teeth on their inside surfaces for producing the required clamping force. There is the risk that the teeth will cut into the surface of the stranded cable and damage its wires.